Variability of young stars with LSST Gregory J. Herczeg KIAA

Star Formation: ISM/Molecular Clouds

Pre-main sequence stellar evolution (low-mass case) HD141569, Clampin et al. Classical T Tauri Stars

From Visser et al., in prep

Morphology of a classical T Tauri star Dullemond et al., PPV

Morphology of a classical T Tauri star

Luminosities much lower than predicted from steady infall Possible solution: most stellar mass accretes during rare outbursts Luminosity Problem (Kenyon et al. 1990; Dunham, Evans, et al. 2009/2010) T bol L bol

Young Star Outbursts FUors and EXors Very rare -~10 confirmed FUors 5-8 magnitude increase in luminosity EXors: 1 year duration FU Ori: 1937 outburst is still ongoing Miller et al Palomar Transient Factory

Accretion Variability: EX Lup McLaughlin (1946)

2008 Outburst of EX Lup 5-magnitude brightness – 2 x M sol /yr – 100 times higher than quiescence Lasted about half a year – Similar strength, duration as 1955 outburst Aspin et al. 2010

Accretion-powered jets Episodic mass ejection: related to accretion events? (e.g., Reipurth et al. 1989)

Accretion Histories Rate and strength of FUOr/EXOr outbursts – Limited to end state of accretion – Class 0/I: JCMT/SCUBA2? Identify physical cause of outbursts – Gravitational Instability + MRI (Zhu et al. 2010) – Multiple star/disk interactions (Reipurth et al.) – Thermal Instability (Martin et al. 2010) – Gravitational Clumping (Vorobyov & Basu 2005)

Optical accretion diagnostics

Accretion columns of AA Tau (Bouvier et al. 2007) H-alpha line profiles V-band periodicity

Variable accretion onto young star with disk (Herczeg et al. in prep)

COROT observations of NGC 2264 (Alencar, Bouvier, et al. 2010) NO DISK DISK ACCRETION Stochastic variability: changes in star-disk interaction Longer term variability: disk instabilities

Disks Warps (e.g., Herbst et al. 2000s; Plavchan et al. 2008) I-magnitude through 5 different seasons

Ongoing SF variability programs COROT observations of NGC 2264 (Alencar et al.) YSOVar: Warm Spitzer near-IR monitoring (Stauffer et al.) Palomar Transit Factory (Hillenbrand, Covey) VYSSOS: daily monitoring of many SF regions (P.I. Reipurth; not yet ongoing, uncertain future) PAN-STARRS

Young star variability Accretion history (for optically visible objects) Accretion variability: unbiased assessment, timescales Rotational modulation (space-based monitoring best) Disk warps: planet-induced, star/disk interactions Light echoes: outburst bouncing off envelope, disk Hot spots of magnetically active M-dwarfs Eclipsing binaries as test of stellar evolution tracks LSST, not variability (covered by VISTA?) Low-metallicity galactic star formation (Yasui et al. 2009) Extinction mapping Young populations/IMF (need complementary spectra)

Formation of youngest disks (Herczeg et al. 2011) VLT/CRIRES M-band spectra of CO emission -R = 100,000 -Usually behind AO Measure CO emission/profiles from disks around protostars Disks: either present or absent

Searching for growth of disks (Herczeg et al. 2012) Watson et al. 2007, Nature Spitzer/IRS spectra: hot water emission from envelope/disk accretion shock? Herschel far-IR spectral imaging: hot water emission from the outflow, not the disk

UV Excess Measures of Accretion (Herczeg, in prep) Low-resolution optical spectra of 300 T Tauri stars – Palomar and Keck – A, R=1000 – Largest U-band spectroscopic sample of T Tauri stars to date Most accurate method to measure accretion rate -Simultaneous extinction, spectral type 80 more spectra from VLT/X-Shooter 3000 A – 2.5 microns at R=10,000

Disks, Accretion and Outflows from T Tauri stars (DAO of Tau) (P.I. Herczeg) HST/FUV spectra – A – R=20,000 – 30 stars, 111 orbits total) Hot emission from accretion shock Molecular emission from disks Wind absorption lines Discovery of FUV CO Emission from T Tauri stars, France et al. (2011)

Variability of young stars Accretion history for visible objects Accretion variability: unbiased assessment, timescales Rotational modulation (space-based monitoring best) Disk warps: planet-induced, star/disk interactions Light echoes: outburst bouncing off envelope structures Hot spots of magnetically active M-dwarfs Eclipsing binaries as test of stellar evolution tracks LSST, not variability Low-metallicity SF (e.g., Yasui et al.) Extinction mapping Young populations: need spectra (SpT, gravity, better ages)